Our objectives are: 1) to determine the airway changes which increase upper airway resistance during sleep and to identify and study brain stem regions which control the patency of the upper airway; and 2) to characterize the changes in blood and cerebral spinal fluid acid-base balance during sleep and wakefulness. To these ends we will use acute and chronic cats recorded in sleep and wakefulness to: 1) record upper airway muscle activity and correlate this activity with changes in airway resistance; 2) map the brain stem with stimulating electrodes to delineate regions which influence the respiratory activity of the muscle of the upper airway; 3) lesion brain stem areas shown to influence airway patency in an attempt to create an animal model of obstructive sleep apnea; 4) record single neurons in regions shown to influence the respiratory activity of upper airway muscles in an effort to better understand the central control of the upper airways; 5) measure blood and CSF acid-base composition using conventional electrode techniques; 6) measure cerebral blood flow using radioactive microspheres; 7) calculate cerebral metabolic rate by the Fick principle with measured 02 content of arterial and sagittal sinus blood and cerebral blood flow rate; 8) measure respiratory gas exchange using conventional gas analyzers. The significance of these experiments derives from the recent emergence of a group of sleep apnea syndromes, particularly obstructive sleep apneas. An understanding of their pathophysiology requires techniques which are possible only in animal experiments. Upper airway resistance increases during sleep in the cat. The mechanisms of this increase may relate to obstructive sleep apnea. Blood gas experiments are essential to know the effects of change in breathing patterns which occur in sleep and wakefulness. They will provide a basis for understanding changes in the chemical environment which may lead to cardiac and hemodynamic irregularities in apneic patients.